Many marine algae and certain flowering plants accumulate 3-dimethylsulfoniopropionate (DMSP). This is of both environmental and agricultural interest. The environmental interest arises because DMSP is the major biogenic source of atmospheric dimethyl sulfide (DMS), which has a central role in the global sulfur cycle. Biogenic DMS is also implicated in acid precipitation and, as the main source of cloud condensation nuclei over the oceans, may be involved in climate regulation. The agricultural interest stems from the effectiveness of DMSP as an osmoprotectant and cryoprotectant and from the possibility of enhancing the stress resistance of crops by genetic engineering of the accumulation of such compounds. Despite the importance of DMSP, little is known about its biosynthetic pathway and the enzymes involved. For the higher plant Wollastonia biflora we have shown that the biosynthetic pathway involves the following steps: methionine - S-methylmethionine - dimethylsulfonio-propionaldehyde - DMSP.